The disclosure of Japanese Patent Application No. 11-304388 filed on Oct. 26, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an exhaust temperature raising apparatus and method for an internal combustion engine.
2. Description of the Related Art
Diesel engines produce large amounts of unburned HCs during low-load engine operations, and particularly during a warm-up operation, since the combustion chamber temperature is low during such operations.
There is a known technology in which an exhaust control valve is disposed in an engine exhaust passage, and the combustion chamber temperature is raised by closing the exhaust control valve and increasing the amount of fuel injected, so as to curb production of unburned HCs (see, for example, Japanese Patent Application Laid-Open No. SHO 49-80414).
When the exhaust control valve is substantially completely closed after the combustion chamber temperature has been raised by increasing the amount of fuel injected as mentioned above, the pressure in the exhaust passage, that is, the back pressure, becomes considerably high. If the back pressure is high, the exhaust gas temperature is unlikely to decrease, so that exhaust gas in the exhaust passage remains in a high temperature state. Furthermore, if the back pressure rises, the exhaust gas flow rate decreases, so that high-temperature exhaust gas resides or dwells in a portion of the exhaust passage upstream of the exhaust control valve. While exhaust gas resides in this fashion, the exhaust gas is in a high-temperature state. As a result, unburned HCs among the exhaust gas components are oxidized, and the amount of unburned HCs contained in exhaust gas emitted into the atmosphere is reduced.
In another technology for lessening unburned HCs, an emission control catalyst is disposed in an engine exhaust passage. However, unless activated, the catalyst is unable to sufficiently control emission, that is, unable to lessen unburned HCs.
There is a well-known technology in which in addition to main injection, that is, fuel injection for producing the engine output, sub-injection, that is, subsidiary fuel injection after the main injection, is performed during the expansion stroke (see, for example, Japanese Patent Application Laid-Open Nos. HEI 8-303290 and HEI 10-212995).
If the sub-injection is performed in addition to the main injection, unburned HCs produced by the combustion attributed to the main injection (hereinafter, referred to as xe2x80x9cmain combustionxe2x80x9d) are burned in the combustion attributed to the sub-injection (hereinafter, referred to as xe2x80x9csub-combustionxe2x80x9d), so that the amount of unburned HCs itself decreases to a considerably low level. Furthermore, since unburned HCs produced by the main combustion burn together with the sub-injection fuel, the amount of combustion increases. As a result, the exhaust gas temperature rises so that a high catalyst temperature is achieved. Thus, the amount of unburned HCs is reduced.
Although various technologies for lessening unburned HCs have been proposed, further reduction of the amount unburned HCs is still raised as a great issue.
Therefore, the present inventors, through experiments and researches, conceived of performing the main fuel injection in an excess-air condition, and after the main fuel injection, the sub-injection is performed to increase the amount of combustion, and an exhaust control valve provided in an exhaust passage is substantially completely closed.
Due to the synergetic effect of the combustion attributed to the subsidiary injection and the exhaust throttling in this design, the oxidation of unburned HCs in the combustion chamber is accelerated and the temperature in the exhaust passage becomes high, so that the amount of unburned HCs is considerably reduced. Therefore, a considerable reduction in the proportion of unburned HCs to the total amount of exhaust gas components emitted into the atmosphere can be expected.
Based on verification of the above-described effect through experiments and researches, the present applicant has already applied for a patent regarding a technology for lessening unburned HCs by performing the main fuel injection in an excess-air condition, and performing, after the main fuel injection, the subsidiary fuel injection to increase the amount of combustion, and, in addition, by providing an exhaust control valve in an exhaust passage and operating the valve to a substantially completely closed state.
Whether unburned HCs have been normally lessened is determined based on detection values provided by various sensors, for example, an exhaust gas temperature sensor, a back pressure sensor, etc. It is conceivable that a failure in any one of the sensors can adversely affect the exhaust gas temperature. If such a sensor fails, the exhaust gas temperature cannot be monitored, so that the exhaust gas temperature control becomes impossible. As a result, the exhaust gas temperature does not remain in a temperature range of a target level (hereinafter, referred to as xe2x80x9ctarget exhaust gas temperaturexe2x80x9d), so that production of unburned HCs may not be curbed.
The target exhaust gas temperature refers to an exhaust gas temperature which is sufficiently high to promote oxidation of unburned HCs, that is, generally-termed post-combustion, and which is not excessively high and therefore, if a catalyst is provided in an exhaust passage, will not cause heat deterioration of the catalyst.
Furthermore, due to a failure or defect in a fuel injection valve or a fuel injection valve control apparatus, as for example, a sufficient amount of fuel may not be injected, and therefore the exhaust gas temperature may not reach the target exhaust gas temperature, or the amount of fuel injected may be excessively large, and therefore the exhaust gas temperature may exceed the target exhaust gas temperature.
Still further, it is also conceivable that due to, for example, a sensor failure or the like, it is falsely determined that the exhaust gas temperature has not reached the target exhaust gas temperature although the exhaust gas temperature is actually higher than the target exhaust gas temperature. In such a case, an engine control unit (hereinafter, referred to as xe2x80x9cECUxe2x80x9d) will determine that it is necessary to burn more fuel in order to bring the exhaust gas temperature to the target exhaust gas temperature. Therefore, the catalyst may deteriorate due to overheating, or the amount of HCs produced may increase more than necessary.
Accordingly, it is an object of the invention to provide an internal combustion engine exhaust temperature raising apparatus and method capable of detecting an abnormality in sensors, fuel injection valves, or the like during an early period and therefore capable of preventing an increase in the amount of unburned HCs in exhaust gas and, if a catalyst is provided in the exhaust passage, preventing heat deterioration of the catalyst.
In accordance with a first aspect of the invention, an exhaust temperature raising apparatus for an internal combustion engine includes an exhaust throttle valve that is provided in an exhaust passage of the internal combustion engine and that adjusts an amount of an exhaust gas flowing in the exhaust passage based on an amount of throttling by the exhaust throttle valve, a fuel injection valve that performs a main injection that is a fuel injection for producing an engine output and a sub-injection that is a subsidiary fuel injection after performance of the main injection, directly into a cylinder, exhaust gas temperature increase means for, during an engine operation during which a need to lessen an unburned fuel component contained in the exhaust gas is high, performing and controlling exhaust throttling by the exhaust throttle valve and performing and controlling an exhaust gas temperature increase through combustion attributed to the main injection performed in an excess-air condition by the fuel injection valve and combustion attributed to the sub-injection, exhaust gas temperature increase monitor means for monitoring a state of temperature increase of the exhaust gas caused by performance of the exhaust gas temperature increase means, monitor means abnormality determination means for determining whether the exhaust gas temperature increase monitor means has an abnormality, and exhaust gas temperature increase stop means for stopping an operation of the exhaust gas temperature increase means when the monitor means abnormality determination means determines that the exhaust gas temperature increase monitor means has an abnormality.
Examples of the aforementioned xe2x80x9can engine operation during which a need to lessen an unburned fuel component contained in the exhaust gas is highxe2x80x9d include a low-speed and low-load operation of the engine and, more particularly, a warm-up operation of the engine.
The phrase xe2x80x9cperforming and controlling exhaust throttling by the exhaust throttle valvexe2x80x9d regarding the exhaust gas temperature increase means refers to closing the exhaust throttle valve to such a degree that an unburned fuel component, for example, unburned HCs, can be effectively lessened in conjunction with performance of combustion based on the main injection and the sub-injection; for example, it refers to closing the exhaust throttle valve to a completely closed state or a nearly completely closed state.
The xe2x80x9cexhaust gas temperature increase meansxe2x80x9d includes the exhaust throttle valve, the fuel injection valve, and an ECU that controls the operation of the exhaust throttle valve and the operation of the fuel injection valve.
The xe2x80x9cexhaust gas temperature increase monitor meansxe2x80x9d includes at least one sensor, such as a temperature sensor.
The xe2x80x9cmonitor means abnormality determination meansxe2x80x9d and the xe2x80x9cexhaust gas temperature increase stop meansxe2x80x9d includes an ECU.
In this invention, when the exhaust gas temperature increase means is operated, exhaust gas temperature increases due to combustion attributed to the main injection in an excess-air condition and combustion attributed to the sub-injection. Therefore, exhaust gas discharged from the cylinder of the internal combustion engine has an increased temperature. Furthermore, a high-temperature state of exhaust gas is maintained in the exhaust passage by exhaust throttling. Therefore, the oxidation of unburned HCs is promoted in the exhaust passage, so that the amount of unburned HCs can be reduced.
The invention further achieves the following advantage. If, during the exhaust temperature raising control by the exhaust gas temperature increase means, it is determined by the monitor means abnormality determination means that the exhaust gas temperature increase monitor means is in a state in which the means cannot carry out the expected function thereof due to a failure or the like of the means (an abnormal state), the exhaust gas temperature increase stop means stops the operation of the exhaust gas temperature increase means. Therefore, the exhaust temperature raising control by the exhaust gas temperature increase means is stopped.
Therefore, it is possible to prevent unexpected increases in the amount of combustion caused by occurrence of an abnormal state, such as the aforementioned failure or the like. Thus, the apparatus is able to prevent an unexpected increase in the amount of unburned HCs and, if a catalyst is provided in the exhaust passage, prevent heat deterioration of the catalyst caused by an abnormal exhaust temperature increase.
In accordance with a second aspect of the invention, an exhaust temperature raising apparatus for an internal combustion engine includes an exhaust throttle valve that is provided in an exhaust passage of the internal combustion engine and that adjusts an amount of an exhaust gas flowing in the exhaust passage based on an amount of throttling of the exhaust throttle valve; a fuel injection valve that performs a main injection that is a fuel injection for producing an engine output and a sub-injection that is a subsidiary fuel injection after performance of the main injection, directly into a cylinder, exhaust gas temperature increase means for, during an engine operation during which a need to lessen an unburned fuel component contained in the exhaust gas is high, performing and controlling exhaust throttling by the exhaust throttle valve and performing and controlling an exhaust gas temperature increase through combustion attributed to the main injection performed in an excess-air condition by the fuel injection valve and combustion attributed to the sub-injection, exhaust gas temperature increase monitor means for monitoring a state of temperature increase of the exhaust gas caused by performance of the exhaust gas temperature increase means, exhaust gas temperature increase abnormality determination means for determining whether there is an abnormality regarding the state of temperature increase of the exhaust gas monitored by the exhaust gas temperature increase monitor means, and exhaust gas temperature increase stop means for stopping an operation of the exhaust gas temperature increase means when the exhaust gas temperature increase abnormality determination means determines that there is an abnormality regarding the state of temperature increase of the exhaust gas.
The aforementioned xe2x80x9can engine operation during which a need to lessen an unburned fuel component contained in the exhaust gas is highxe2x80x9d, xe2x80x9cexhaust gas temperature increase meansxe2x80x9d, xe2x80x9cperforming and controlling exhaust throttling by the exhaust throttle valvexe2x80x9d regarding the exhaust gas temperature increase means, xe2x80x9cexhaust gas temperature increase monitor meansxe2x80x9d, and xe2x80x9cexhaust gas temperature increase stop meansxe2x80x9d are substantially the same as described above in conjunction with the first aspect.
The xe2x80x9cexhaust gas temperature increase abnormality determination meansxe2x80x9d includes an ECU.
In this aspect, too, the temperature of exhaust gas is increased by performance of the exhaust gas temperature increase means, so that the amount of unburned HCs can be reduced. The exhaust temperature raising apparatus also achieves the following advantages.
If, due to a problem in the exhaust gas temperature increase means, more specifically, a problem caused by a failure in, for example, a fuel injection valve, that is, a component of the exhaust gas temperature increase means, the fuel injection valve supplies an excessively large amount of fuel so that the amount of combustion in the cylinder increases and the exhaust gas temperature becomes excessively higher than a target exhaust gas temperature, the exhaust gas temperature increase abnormality determination means in this aspect of the invention determines that there is an abnormality regarding the state of exhaust gas temperature increase, and then the exhaust gas temperature increase stop means stops the operation of the exhaust gas temperature increase means. At the time of the stop, therefore, undesired excessive combustion in the cylinder discontinues. Hence, the apparatus is able to prevent an increase in the amount of HCs caused by undesired excessive combustion and, if a catalyst is provided in the exhaust passage, prevent heat deterioration of the catalyst.
In the second aspect, when the exhaust gas temperature increase abnormality determination means determines that there is an abnormality regarding the state of temperature increase of the exhaust gas, it may be determined that the exhaust gas temperature increase means has an abnormality, and the operation of the exhaust gas temperature increase means may be stopped.
In the first and second aspects, the exhaust gas temperature increase monitor means may include an exhaust gas temperature sensor provided at a suitable location in the exhaust passage, and the exhaust gas temperature increase monitor means may monitor the state of temperature increase of the exhaust gas based on an exhaust gas temperature detected by the exhaust gas temperature sensor. The suitable location at which the exhaust gas temperature sensor is provided may be, for example, a location in the exhaust passage upstream of the exhaust throttle valve.
In the first and second aspects, the exhaust gas temperature increase monitor means may include a back pressure sensor provided at a location in the exhaust passage upstream of a location of the exhaust throttle valve, and the exhaust gas temperature increase monitor means may monitor the state of temperature increase of the exhaust gas based on a back pressure detected by the back pressure sensor.
The back pressure sensor is included in the exhaust gas temperature increase monitor means because changes in the back pressure are in association with changes in the exhaust gas temperature.
In the first and second aspects, the exhaust gas temperature increase monitor means may include a back pressure sensor and an exhaust gas temperature sensor that are provided in a portion of the exhaust passage upstream of the exhaust throttle valve. When a value detected by the back pressure and a value detected by the exhaust gas temperature sensor are within their respective target ranges, the monitor means abnormality determination means may determine that there is no abnormality regarding the state of temperature increase of the exhaust gas.
The target range of the back pressure refers to values of back pressure that are included within such a range that the exhaust gas temperature is likely to reach the target exhaust gas temperature during the exhaust temperature raising control. The back pressure has a great effect on the exhaust gas temperature, so that if a certain exhaust gas temperature can be secured by adjustment of the back pressure, it becomes easier to bring the exhaust gas temperature to the target exhaust gas temperature.
In the first and second aspects, the exhaust gas temperature increase stop means may stop the operation of the exhaust gas temperature increase means by opening the exhaust throttle valve and stopping performance of the sub-injection.